This invention is generally directed to titanyl phthalocyanines and processes for the preparation thereof, and more specifically the present invention is directed to processes for obtaining titanyl phthalocyanine polymorphs or crystal forms, known as Type I, reference for example U.S. Pat. No. 4,898,799, the disclosure of which is totally incorporated herein by reference, and wherein there can be obtained from the formed Type I, Type IV or similar titanium phthalocyanines which can be selected as a photogenerating pigment for layered photoconductive imaging members. In one embodiment, the present invention is directed to a process for the preparation of Type I titanyl phthalocyanines by the reaction of phthalonitrile and diiminoisindoline with a titanium tetraalkoxide, such as titanium tetraperoxide. The known titanyl phthalocyanines, especially the known polymorph IV and the X form which can be obtained from the aforementioned Type I, can be selected as organic photogenerator pigments in photoresponsive imaging members containing charge, especially hole transport layers such as aryl amine hole transport molecules. The aforementioned photoresponsive imaging members can be negatively charged when the photogenerating layer is situated between the hole transport layer and the substrate, or positively charged when the hole transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductor imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of the appropriate charge. Generally, the imaging members are sensitive in the wavelength regions of from about 700 to about 850 nanometers, thus diode lasers can be selected as the light source. Titanyl phthalocyanines may also be selected as intense blue light-stable colorants for use in coatings, such as paint, inks, and as near infrared absorbing pigments suitable for use as IR laser optical recording materials.
The process of the present invention in one embodiment involves dissolving the Type I titanyl phthalocyanine (TiOPc) pigment obtained in a suitable solvent such as sulfuric acid, trifluoroacetic acid, and the like, or mixtures of trifluoroacetic acid and methylene chloride, followed by a reprecipitation of the dissolved pigment into a second solvent system comprised, for example, of an alcohol such as methanol, water, toluene, tetrahydrofuran, dimethyl formamide, mixtures thereof, and the like. The composition of both the solvent and the precipitant solvent primarily determines which polymorphic form of TiOPc can be obtained. The desired polymorphic form, which can be controlled by the selection of precipitant solvent to provide any one of Type II, III, IV, X or others can be isolated by a simple filtration process whereby the precipitated mixture is poured directly into a porcelain funnel fitted with a glass fiber filter cloth, and can be washed with water and/or organic solvents such as acetone or methanol to attain a suitable degree of purity. More specifically, with tetrahydrofuran, 1 part by weight, and methylene chloride, 4 parts, and the nonsolvent water, 5 parts, Type IV titanyl phthalocyanine can be obtained. Similarly, Type X, III, and II titanyl phthalocyanines can be obtained from Type I by selecting in place of the water methanol-water, 1:1; acetone-water, 1:1; o isopropanol, respectively.
Certain titanium phthalocyanine pigments have been known since at least the publication WW 2(PB 85172 Fiat Final Report 1313, Feb. 1, 1948). However, unlike other phthalocyanines such as metal-free, copper, iron and zinc phthalocyanines, titanium phthalocyanines have, it is believed had minimum commercial use. Titanyl phthalocyanines or oxytitanium phthalocyanines are known to absorb near-infrared light around 800 nonometers and a number of such pigments have been illustrated in the prior art as materials for IR laser optical recording material, reference for example BASF German 3,643,770 and U.S. Pat. No. 4,458,004. Also, the use of certain titanium phthalocyanine pigments as a photoconductive material for electrophotographic applications is known, reference for example British Patent Publication 1,152,655, the disclosure of which is totally incorporated herein by reference. Also, U.S. Pat. No. 3,825,422 illustrates the use of titanyl phthalocyanine as a photoconductive pigment in an imaging process known as particle electrophoresis. Additionally, the utilization of certain titanyl phthalocyanines and substituted derivatives thereof in a dual layer electrographic device is illustrated in EPO 180931, May 14, 1986. Moreover, the use of tetra- and hexadeca-fluoro-substituted titanyl phthalocyanine in an electrophotographic device is illustrated in U.S. Pat. No. 4,701,396. In Japanese Patent Publication 64-171771, August, 1986, there is illustrated the use of titanyl phthalocyanine, which has been treated with a hot solvent, in electrophotography. Further, in German 3,821,628 there is illustrated the utilization of certain titanyl phthalocyanines, and other pigments in electrophotography, and wherein the titanyl phthalocyanines have been purified primarily to reduce the level of ash, volatile contaminants and sodium to below specified levels.
As mentioned in the textbook Phthalocyanine Compounds by Moser and Thomas, the disclosure of which is totally incorporated herein by reference, polymorphism or the ability to form distinct solid state forms is well known in phthalocyanines. For example, metal-free phthalocyanine is known to exist in at least 5 forms designated as alpha, beta, pi, X and tau. Copper phthalocyanine crystal forms known as alpha, beta, gamma, delta, epsilon and pi are also described. These different polymorphic forms are usually distinguishable on the basis of differences in the solid state properties of the materials which can be determined by measurements, such as Differential Scanning Calorimetry, Infrared Spectroscopy, Ultraviolet-Visible-Near Infrared Spectroscopy and, especially, X-Ray Powder Diffraction techniques. There appears to be general agreement on the nomenclature used to designate specific polymorphs of commonly used pigments such as metal-free and copper phthalocyanine. However, this does not appear to be the situation with titanyl phthalocyanines as different nomenclature is selected in a number of instances. For example, reference is made to alpha, beta, A, B, C, y, and m forms of TiOPc (titanyl phthalocyanine) with different names being used for the same form in some situations. It is believed that four main crystal forms of TiOPc are known, that is Types I, II, III, and IV, reference copending application U.S. Ser. No. 533,261 (D/90198), the disclosure of which is totally incorporated herein by reference.
Titanyl phthalocyanine can be classified as indicated in Table 1 that follows:
TABLE 1 ______________________________________ Crystal Other Form Names Documents ______________________________________ Type I .beta. Toyo Ink Electrophotog. (Japan) 27,533 (1988) .beta. Dainippon U.S. Pat. No. 4,728,592 .beta. Sanyo-Shikiso JOP 63-20365 A Mitsubishi JOP 62-25685, -6, -7 Con- ference Proceedings A Konica "Japan Hardcopy 1989", 103, (1989) Type II .alpha. Toyo Ink "Electrophoto (Japan)" 27,533 (1988) .alpha. Sanyo-Shikiso JOP 63-20365 .alpha. Konica U.S. Pat. No. 4,898,799 .alpha. Dainippon U.S. Pat. No. 4,728,592 .alpha. Mita EU 314,100 B Mitsubishi JOP 62-25685, -6, -7 B Konica "Japan Hardcopy 1989, 103, (1989) Type III C Mitsubishi OP 62-25685, -6, -7 C Konica "Japan Hardcopy 1989, 103, (1989) m Toyo Ink "Electrophoto (Japan)" 27,533 (1988) Type IV y Konica "Japan Hardcopy 1989", 103, (1989) Unnamed Konica U.S. Pat. No. 4,898,799 New Type Sanyo-Shikiso JOP 62-20365 ______________________________________
More specifically, the aforementioned documents illustrate, for example, the use of specific polymorphs of TiOPc in electrophotographic devices. Three crystal forms of titanyl phthalocyanine, differentiated by their XRPDs, were specifically illustrated, identified as A, B, and C, which it is believed are equivalent to Types I, II, and III, respectively. In Japanese 62-256865 there is disclosed, for example, a process for the preparation of pure Type I involving the addition of titanium tetrachloride to a solution of phthalonitrile in an organic solvent which has been heated in advance to a temperature of from 160.degree. to 300.degree. C. In Japanese 62-256866, there is illustrated, for example, a method of preparing the aforementioned polymorph which involves the rapid heating of a mixture of phthalonitrile and titanium tetrachloride in an organic solvent at a temperature of from 100.degree. to 170.degree. C. over a time period which does not exceed one hour. In Japanese 62-256867, there is described, for example, a process for the preparation of pure Type II (B) titanyl phthalocyanine, which involves a similar method to the latter except that the time to heat the mixture at from 100.degree. to 170.degree. C. is maintained for at least two and one half hours. Types I and II, in the pure form obtained by the process of the above publications, apparently afforded layered photoresponsive imaging members with excellent electrophotographic characteristics.
In Mita EPO Patent Publication 314,100, there is illustrated the synthesis of TiOPc by, for example, the reaction of titanium alkoxides and diiminoisoindoline in quinoline or an alkylbenzene, and the subsequent conversion thereof to an alpha Type pigment (Type II) by an acid pasting process, whereby the synthesized pigment is dissolved in concentrated sulfuric acid, and the resultant solution is poured onto ice to precipitate the alpha-form, which is filtered and washed with methylene chloride. This pigment, which was blended with varying amounts of metal free phthalocyanine, could be selected as the electric charge generating layer in layered photoresponsive imaging members with a high photosensitivity at, for example, 780 nanometers.
In Sanyo-Shikiso Japanese 63-20365/86, reference is made to the known crystal forms alpha and beta TiOPc (Types II and I, respectively, it is believed), which publication also describes a process for the preparation of a new form of titanyl phthalocyanine, which is apparently not named. This publication appears to suggest the use of the unnamed titanyl phthalocyanine as a pigment and its use as a recording medium for optical discs. This apparently new for was prepared by treating acid pasted TiOPc (Type II form, it is believed) with a mixture of chlorobenzene and water at about 50.degree. C. The resulting apparently new form is distinguished on the basis of its XRPD, which appears to be identical to that shown in FIG. 1 for the Type IV polymorph.
In U.S. Pat. No. 4,728,592, there is illustrated, for example, the use of alpha type TiOPc (Type II) in an electrophotographic device having sensitivity over a broad wavelength range of from 500 to 900 nanometers. This form was prepared by the treatment of dichlorotitanium phthalocyanine with concentrated aqueous ammonia and pyridine at reflux for 1 hour. Also described in the aforementioned patent is a beta Type TiOPc (Type I) as a pigment, which is believed to provide a much poorer quality photoreceptor.
In Konica Japanese 64-17066/89, there is disclosed, for example, the use of a new crystal modification of TiOPc prepared from alpha type pigment (Type II) by milling it in a sand mill with salt and polyethylene glycol. This pigment had a strong XRPD peak at a value of 2 theta of 27.3 degrees. This publication also discloses that this new form differs from alpha type pigment (Type II) in its light absorption and shows a maximum absorbance at 817 nanometers compared to alpha-type, which has a maximum at 830 nanometer. The XRPD shown in the publication for this new form is believed to be identical to that of the Type IV form previously described by Sanyo-Shikiso in JOP 63-20365. The aforementioned Konica publication also discloses the use of this new form of TiOPc in a layered electrophotographic device having high sensitivity to near infrared light of 780 nanometers. The new form is indicated to be superior in this application to alpha type TiOPc (Type II). Further, this new form is also described in U.S. Pat. No. 4,898,799 and in a paper presented at the Annual Conference of Japan Hardcopy in July 1989. In this paper, this same new form is referred to as Type y, and reference is also made to Types I, II, and III as A, B, and C, respectively.
In the journal, Electrophotography (Japan) vol. 27, pages 533 to 538, Toyo Ink Manufacturing Company, there is disclosed, for example, alpha and beta forms of TiOPc (Types I and II, it is believed) and also this journal discloses the preparation of a Type m TiOPc, an apparently new form having an XRPD pattern which was distinct from other crystal forms. It is believed that this XRPD is similar to that for the Type III titanyl phthalocyanine pigment but it is broadened most likely as the particle size is much smaller than that usually found in the Type III pigment. This pigment was used to prepare photoreceptor devices having greater sensitivity at 830 nanometers than alpha or beta Type TiOPc (Type II or I, respectively).
Processes for the preparation of specific polymorphs of titanyl phthalocyanine, which require the use of a strong acid such as sulfuric acid, are known, and these processes, it is believed, are not easily scable. One process as illustrated in Konica Japanese Laid Open on Jan. 20, 1989 as 64-17066 (U.S. Pat. No. 4,643,770 appears to be its equivalent), the disclosure of which is totally incorporated herein by reference, involves, for example, the reaction of titanium tetrachloride and phthalodinitrile in 1-chloronaphthalene solvent to produce dichlorotitanium phthalocyanine which is then subjected to hydrolysis by ammonia water to enable the Type II polymorph. This phthalocyanine is preferably treated with an electron releasing solvent such as 2-ethoxyethanol, dioxane, N-methylpyrrolidone, followed by subjecting the alpha-titanyl phthalocyanine to milling at a temperature of from 50.degree. to 180.degree. C. In a second method described in the aforementioned Japanese Publication, there is disclosed the preparation of alpha type titanyl phthalocyanine with sulfuric acid. Another method for the preparation of Type IV titanyl phthalocyanine involves the addition of an aromatic hydrocarbon, such as chlorobenzene solvent to an aqueous suspension of Type II titanyl phthalocyanine prepared by the well known acid pasting process, and heating the resultant suspension to about 50.degree. C. as disclosed in Sanyo-Shikiso Japanese 63-20365, Laid Open Jan. 28, 1988. In Japanese 171771/1986, Laid Open Aug. 2, 1986, there is disclosed the purification of metallophthalocyanine by treatment with N-methylpyrrolidone.
To obtain a TiOPc-based photoreceptor having high sensitivity to near infrared light, it is believed necessary to control not only the purity and chemical structure of the pigment, as is generally the situation with organic photoconductors, but also to prepare the pigment in the correct crystal modification. The disclosed processes used to prepare specific crystal forms of TiOPc, such as Types I II, III and IV, are either complicated and difficult to control as in the preparation of pure Types I and II pigment by careful control of the synthesis parameters by the processes described in Mitsubishi Japanese 62-25685, -6 and -7, or involve harsh treatment such as sand milling at high temperature, reference Konica U.S. Pat. No. 4,898,799; or discussion of the pigment in a large volume of concentrated sulfuric acid, a solvent which is known to cause decomposition of metal phthalocyanines, reference Sanyo-Shikiso Japanese 63-20365 and Mita EPO 314,100.
In a patentability search report the following U.S. patents were listed: U.S. Pat. No. 3,927,026, which discloses a process for the preparation of X-form metal phthalocyanine by mixing phthalonitrile in an alkylalkanolamine, adding ammonia, seeding the mixture with a catalytic amount of X-form phthalocyanine, adding a metal salt, and refluxing, see the Abstract of the Disclosure for example; U.S. Pat. No. 4,771,133 which discloses, for example, a process for the preparation of vanadyl phthalocyanine for electrophotographic devices by reacting vanadium pentoxide and phthalonitrile, see the Abstract of the Disclosure, and as background interest U.S. Pat. Nos. 4,443,528; 4,664,997; 4,725,519; 4,728,592; 4,777,251 and 4,898,799.
The present invention in embodiments thereof are directed to economical methods for the preparation of Type I titanyl phthalocyanine in acceptable yield and of high purity and the subsequent conversion of this material into other known titanyl phthalocyanine polymorphic forms, which methods can be considered an improvement over the prior art in that, for example, they are not complex in that no sophisticated equipment, such as a glass-lined reactor is required for the addition of dangerous or volatile materials such as titanium tetrachloride or concentrated sulfuric acid, are rapid in that reaction times are on the order of two hours as compared to six to eight hours illustrated in a number of the prior art teachings, and do not require the use of harsh reagents such as sulfuric acid or the use of energy intensive processes such as sand milling. Other advantages of the present invention are as illustrated herein.
Layered photoresponsive imaging members are described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, wherein there is illustrating an imaging member comprised of a photogenerating layer, and an aryl amine hole transport layer. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Moreover, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions.
In copending application U.S. Ser. No. 537,714 filed Jun. 14, 1990 (D/90087), the disclosure of which is totally incorporated herein by reference, there are illustrated photoresponsive imaging members with photogenerating titanyl phthalocyanine layers prepared by vacuum deposition. It is indicated in this copending application that the imaging members comprised of the vacuum deposited titanyl phthalocyanines and aryl amine hole transporting compounds exhibit superior xerographic performance as low dark decay characteristics results and higher photosensitivity is generated, particularly in comparison to several prior art imaging members prepared by solution coating or spray coating, reference for example U.S. Pat. No. 4,429,029 mentioned hereinbefore.
In copending application U.S. Ser. No. 533,265, filed Jun. 4, 1990, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of phthalocyanine composites which comprises adding a metal free phthalocyanine, a metal phthalocyanine, a metalloxy phthalocyanine or mixtures thereof to a solution of trifluoroacetic acid and a monohaloalkane; adding to the resulting mixture a titanyl phthalocyanine; adding the resulting solution to a mixture that will enable precipitation of said composite; and recovering the phthalocyanine composite precipitated product.
Also in copending application U.S. Ser. No. 533,261, filed Jun. 4, 1990, the disclosure of which is totally incorporated herein by reference, there are illustrated various types of phthalocyanines and processes for the preparation thereof. One embodiment of the aforementioned copending application is directed to processes for the preparation of titanyl phthalocyanines, which comprise the addition of 1,3-diiminoisoindoline, which is considered a costly reactant, to N-methylpyrrolidone and titanium tetrapropoxide, see Example I, to provide Type I or .beta.-type titanyl phthalocyanine as determined by X-ray powder diffraction; dissolving the resulting titanyl phthalocyanine in a mixture of trifluoroacetic acid and methylene chloride; adding the resulting mixture to a stirred organic solvent, such as methanol, or to water; separating the resulting precipitate by, for example, vacuum filtration through a glass fiber paper in a Buchner funnel; and washing the titanyl phthalocyanine product.
Diiminoisoindoline, especially the 1,3 form (DI.sup.3), is not readily commercially available, but can be obtained at a cost of about $1,000 per kilogram, and with the present invention in embodiments less, as much as 90 percent, for example, diiminoisoindoline may be selected, or with the ammonium process illustrated herein the use of diiminoisoindoline can be avoided. The phthalonitrile reactant utilized is substantially less costly, for example about $20 per kilogram. Generally, to obtain acceptable yields, for example, from about 50 to about 95 percent, of titanyl phthalocyanine using phthalonitrile, it is necessary to react it with titanium tetrachloride. This reagent is strongly corrosive and reactive in the air, emitting toxic fumes. A consequence of its corrosive nature is that it usually is not used in conventional metal reactors which are desirable for large scale preparations. Another serious drawback to the use of TiCl.sub.4 to synthesize Type I TiOPc is that it can result in the formation of chlorinated phthalocyanine byproduct which cannot be readily removed from the product (reference, for example, the hereinbefore mentioned publication by Konic: Japan Hardcopy, 1989, page 103). This latter problem renders the Type I titanyl phthalocyanine obtained undesirable for use in layered photoconductive devices in which highly pure grades of pigment are required. The process of the present invention avoids, or minimizes the aforementioned problems. Further, the titanium tetraalkoxides, such as titanium-tetrapropoxide and titanium-tetrabutoxide, selected as reactants for the process of the present invention are relatively noncorrosive and remain stable with oxidation or hydrolysis when exposed to room temperature air for the length of time required to add them to the solution, from about 1/2 minute to about 15 minutes and typically about 1 minute. The yield of Type I TiOPc obtained when the aforementioned reagents are reacted with phthalonitrile under a variety of conditions is usually unacceptably low, being about 15 percent. With the processes of the present invention, in embodiments the use of small amounts of the reactant 1,3-diiminoisoindoline can result in higher yields of, for example, from about 60 to about 80 percent. Also, a number of the prior art teachings disclose the use of diiminoisoindoline and titanium tetrapropoxide or the use of phthalonitrile with titanium tetrachloride in high boiling and malodorous solvents such as chloronaphthalene and quinoline, as the preferred method in the synthesis photoreceptor-grade TiOPc. The process of the present invention in embodiments permits a greater number of solvents to be used, including the non-odorous N-methyl pyrrolidone.
The disclosures of all of the aforementioned publications, laid open applications, pending applications, and patents are totally incorporated herein by reference.